The invention relates to a method for treating particulate material with a coating medium, in particular for sugarcoating or film-coating of pharmaceutical or food preformed pieces, wherein the material is filled into a container, moved in the container by rotating the container, sprayed with the coating medium and the sprayed coating medium is dried by process air.
The invention further relates to an apparatus for carrying out the method comprising a container drivable to rotate about an axis, a spraying device for spraying the coating medium onto the material and supplying means for supplying process air.
Such a method and apparatus are known from the published German patent application DE 1 198 187.
Such methods and apparatus are used in the pharmaceutical, chemical, confectionary and food industries. In the pharmaceutical industry, medications are produced by sugarcoating making use of a sugared syrup. Film or polished tablets are produced on the other hand by film-coating, which are medications coated with a polymer coating.
The present invention however is not limited to sugarcoating or film coatings, but can also be used in granulation, where fine particles are coated with a medium to agglomerate the particles with one another.
In sugarcoating, the preformed pieces are normally coated with a sticky suspension or solution. In conventional methods, the particulate material to be coated is moved in a rotating container and the coating medium, i.e. the sticky suspension is poured onto the moving material in cycles. In further individual cycles, a distribution follows by which the suspension is uniformly distributed on the particulate material and subsequently, the coating medium is dried. These individual cycles each require about 5 to 10 minutes. After drying, the cycles of pouring, distributing, drawing, etc. are repeated.
In more recent methods for sugarcoating, the coating medium is sprayed onto the particulate material moved in the rotating container by means of a spray nozzle system.
In conventional methods of film-coating, the material to be coated is also moved in a rotating container and sprayed with the coating medium through a nozzle system, the coating medium normally being a solution, dispersion or a viscous suspension in the film-coating method. Subsequently, the material is dried.
The quality of the final coating of the particulate material depends on a uniform, rapid, however gentle circulation of the material to be coated, both in the sugarcoating and film-coating procedures. How the material is circulated in the container also has a considerable influence on the possible ways of applying the coating medium and the effectivity of drying. The application and drying in turn significantly influence the quality of the coating of the finally coated material.
A dragxc3xa9e vessel is known from the above-mentioned German patent application DE 1 198 187 for producing dragxc3xa9es for the confectionary and the pharmaceutical industry. A polishing arm is arranged in the dragxc3xa9e vessel which is connected to the open edge of the vessel or is driven by a shaft lying within the drive shaft of the dragxc3xa9e vessel. The dragxc3xa9e vessel is rotatable about an axis which is inclined to the vertical by an angle.
In the method carried out in this known dragxc3xa9e vessel, the material to be coated is moved in a container which is rotated about an inclined axis. The particulate material is circulated within itself due to the rotation of the container about its axis by which the material is mechanically carried along the rotating wall of the container. Thus descending layers of the material flow downwards on the layers ascending on the rotating wall. Due to the inclined disposition of the axis, a horizontal circulating motion is overlapped by upwardly inclined centrifugal forces. A disadvantage of this conventional apparatus is its limited capacity because the inclined disposition of the axis only allows a certain loading. In addition, when the charge amount is enlarged, inadequacies result with the supply of process air for drying the coating, because the process air only superficially passes the material which is circulated as a compact volume, however does not penetrate through the material.
For this reason, the apparatus in use today are almost exclusively those having a container rotated about a horizontal axis. These apparatus can be operated with larger charges. The disadvantage of apparatus with containers rotating about a horizontal axis however is that a mixing of the particulate material is less satisfactory due to the lack of centrifugal forces. This disadvantage is compensated by the use of mixing baffles or blades, which however represent a mechanical obstacle and promotes abrasion and therefore a damaging of the preformed pieces.
An apparatus with a container rotating about a horizontal axis is disclosed in the German product brochure of Glatt GmbH, Bxc3xchlmxc3xchle, xe2x80x9cGlatt-Coater Type GC400-2000xe2x80x9d.
Moving the particulate material to be coated in a container rotating about a horizontal axis is also a disadvantage with respect to spraying the material with the coating medium. Spraying in the known methods and apparatus of this type takes place either by spraying the medium from above onto the material moving therebelow. This so-called top-spray method however has the drawback that it necessarily leads to large spray losses.
To minimize the spray losses, it has therefore been attempted to immerse the spraying device in the circulating material. In apparatus and methods where the material is moved in a container rotated about a horizontal axis, it has however been found that the movement of the material is negatively influenced by the spraying device immersed in the material itself. A uniform movement and mixing of the particulate material is no longer ensured. Since the immersed, stationary, i.e. non-rotating spraying device again represents a mechanical obstacle to the moving material, the moving particles can be damaged by the mechanical obstacle due to too large friction.
In addition, the published German patent application DE 1 938 797 discloses an apparatus for coating granular material, such as pills, having a container for receiving the granular material and the coating material. The container is formed by a bottom shell rotatable about its middle point and a stationary drum joining with its inner surface to the periphery of the bottom shell smoothly in upward direction. According to the described method, the material to be coated is placed on the bottom shell and rotated at a speed such that the granular material is moved upwardly along the inner surface of the drum by centrifugal forces and from there is moved in circulation back to the bottom shell. The coating material is applied to the granular material circulating in this manner and drying air is blown in between the granular material. In this known apparatus, only the bottom of the container rotates, while the drum is stationary. A disadvantage is that the movement and mixing of the particulate material is insufficient. In addition, the upward moving material caused by centrifugal action flows back in counterflow to the ascending particles in this known method and apparatus. Impacts between the individual particles can cause damage, in particular when the granular particles are brittle. In addition, the ventilation with process air is not optimal in this type of method.
A multistage method is disclosed in the published German patent application DE 27 50 696 for applying a sprayable agent on a material composed of granular, flake, chip or fiber particles. The spray agent is sprayed onto the inner side of a curtain of particles formed to be rotationally symmetric to a vertical axis, which is made up of free falling particles or particles accelerated downwardly. The method is particularly used for coating wood shavings with a sprayable binding agent. The particles forming the curtain are deflected after passing through the direct spray zone and are thrown outwardly from the geometrical axis of the curtain in the form of a circular fan, such that during this ejection movement they are subjected to the action of part of the spray beam penetrating the particle curtain. Thereafter, they are deflected downwardly and treated further or collected and carried off.
An intermediate container bottom rotatable about a vertical axis is provided in this known apparatus, onto which the chips fall from above. By rotation of the intermediate bottom, the chips are thrown to the outside and then fall downwardly, where they then fall out of the container. The container itself in this apparatus, i.e. more precisely the container wall, is formed to be stationary.
An object of the present invention is therefore to provide an improved method and apparatus of the type mentioned at the out-set which avoids the above-mentioned drawbacks and with which the particulate material can be treated with the coating medium in uniformly high quality.
According to the present invention, the object is achieved by a method for treating particulate material with a coating medium, in particular for sugar coating or film-coating pharmaceutical or food preformed pieces, comprising the steps of:
filling said material into a container;
moving said material in said container by rotating said container;
spraying said coating medium onto said material; and
drying said coating medium sprayed onto said material with process air,
wherein said step of moving said material in said container further comprises moving said material in said container in continuous circulating motion along a bottom of said container from an inner diameter to an outer diameter region of said container, from there along an upstanding wall of said container from a lower region to an upper region of said container and from there along an inclined return surface back to said inner diameter region of said bottom.
Further, according to the present invention this object is achieved by an apparatus for treating particulate material with a coating medium, in particular for sugar coating or film-coating pharmaceutical or food preformed pieces, comprising:
a container drivable to rotate about an axis;
a spraying device for spraying said coating medium onto said material; and
supplying means for supplying process air,
wherein said rotation axis is substantially vertical, and wherein said container further comprises:
a bottom;
an upstanding wall; and
an inclined return surface arranged in said container which extends from an upper region of said container in direction of an inner diameter region of said bottom.
The method and apparatus according to the present invention depart from the concept that the material is to be moved and therefore mixed in a container rotating about a horizontal or inclined axis. Instead, according to the present invention, the particulate material is moved in a container rotating about a vertical rotation axis. The advantage is that centrifugal forces are exploited to move the material, which circulate the material in a centrifugally tangentially rolling movement about the vertical rotation axis of the container, along the bottom substantially horizontally or falling off to the outside and moving substantially vertically along the upstanding wall of the container. In the upper region of the container, the direction of movement of the material is deflected into a downward movement along the return surface, whereby with this guidance of the material according to the present invention, the portion of the material ascending along the wall is a mass flow separated from the portion of the material flowing down along the return surface. Thus the material on the whole is moved in a less compact manner, which allows a more efficient drying of the coating medium. A further advantage of this configuration according to the present invention is that the region between the portion of the material moving along the bottom and the portion of the material returning on the return surface provides a space in which a good process air flow and process air mixing can be formed for drying the material. Due to the return surface, which can be arranged to be stationary in the container, i.e. not rotating, and upon which the particulate material preferably flows down under gravity, and due to the continual outward centrifugal movement of the material on the bottom, the further considerable advantage is achieved that the spraying device can be positioned at a particularly favorable location, for example in the center of the container without representing a mechanical obstacle to the movement of the material. The quality of the finished coated material is substantially improved due to the substantially improved gentle mixing of the material in the method and apparatus according to the present invention.
The object underlying the present invention is therefore completely achieved.
In a preferred embodiment of the method, the moving material is sprayed with the coating medium when flowing off of the return surface to the bottom.
In a preferred embodiment of the apparatus, the spraying device comprises at least one spray nozzle arranged in the region between a lower end of the return surface and the bottom.
The feature has the advantage that the spraying takes place at a particularly favourable location, where the material flowing past the spray nozzle can be sprayed with very high uniformity. A further advantage is that the material can be sprayed at an inner diameter region above the bottom, where the material passes by the spray nozzle with a higher density, so that spray losses are minimized.
In a further preferred embodiment of the method, the coating medium is sprayed annularly and radially outwardly onto the material.
In a further preferred embodiment of the apparatus, the spray nozzle is a radially, annularly spraying spray nozzle, in particular a multi-substance nozzle.
The feature has the particular advantage that the material flowing off of the lower end of the return surface can be sprayed uniformly and completely about its periphery. A further advantage of this feature is that the radially sprayed medium can support the radial outwardly directed movement of the material along the bottom. This effect can further be enhanced with the multi-substance nozzle, where additional support air exits the nozzle with the coating medium.
In a further preferred embodiment of the method, the material is moved along the bottom at a different speed compared to the movement along the wall.
In a further preferred embodiment of the apparatus, the bottom of the container can be placed out of contact with the wall and can be driven at a rotary speed independent of the rotary speed of the wall.
This feature has the advantage that a relative rotary speed can be adjusted between the bottom and the wall of the container, which additionally causes a mixing and rolling movement of the material in the transition region between the outer diameter region of the bottom and the lower region of the wall. The bottom and the wall of the container can even be driven in opposite directions to increase the effect. The retention time in the transition region between the bottom and the wall can be increased by the rolling motion of the material, whereby this region is particularly suited as the active drying zone for drying the coating medium.
In a further preferred embodiment of the method, the process air is passed through the material during its movement along the bottom.
In a further preferred embodiment of the apparatus, the supplying means for the process air comprise a supplying channel opening below the bottom, and the bottom is process air permeable in its inner diameter and/or outer diameter region.
The advantage here, in particular in combination with the before mentioned spraying of the material about centrally in the lower region of the container, is that an effective drying is made possible by flowing air through the material directly after spraying. The drying thus takes place in a region of the container in which the material forms a loosened mass of decreasing particle density due to the centrifugal movement, so that the material can be very effectively flowed through with drying air. On the other hand, the air supplied through the bottom can form an air cushion over the bottom, upon which the material can be moved radially outwardly under rotation along the bottom with reduced friction. In the simplest case, the bottom can be configured with perforations to be air permeable.
In a further preferred embodiment of the method, the process air is passed through the material with a radially outwardly directed component.
In a further preferred embodiment of the apparatus, the bottom is formed of a substantially concentric arrangement of several overlying rings of differing diameter wherein adjacent rings partially overlap with a vertical spacing and wherein the diameter of the rings decreases from bottom to top.
The feature has the advantage that the process air passed through the bottom not only can form an air cushion, but also enhances the radial and turning movement of the material along the bottom due to the radially outward process air flow.
In a further preferred embodiment of the method, the process air is passed through the material as it is moved along the wall of the container.
In a further preferred embodiment of the apparatus, the wall is process air permeable at least in its lower region.
The feature has the advantage that the material is also subjected to a process air flow when ascending along the wall, whereby the drying becomes still more effective.
In a further preferred embodiment of the method, the process air is exclusively passed through the material as it is moved along the wall, without the material moved along the bottom being passed by the process air.
In a further preferred embodiment of the apparatus, the supplying means comprise a supplying channel opening in the region of the wall at the side of the bottom, and wherein the wall is process air permeable in this region.
This feature is of particular advantage in the sugarcoating process, because the material sprayed in the central region of the container after flowing off of the return surface is initially moved along the bottom without drying. The coating material sprayed onto the particles can become uniformly distributed during the movement along the bottom through a fulling effect and thus a coating with uniform thickness is achieved.
In a further preferred embodiment of the method, the process air is also passed through the material when moved back along the return surface.
In a further preferred embodiment of the apparatus, the return surface is process air permeable.
This feature further improves the drying effectiveness, because the particulate material after being sprayed with the coating medium undergoes a two-phase drying by the process air, namely a first time on the bottom, if the bottom is process air permeable, at least however a first time when ascending along the wall and a second time when flowing downwardly along the return surface.
In the method, the process air is preferably heated before passing through the material moving back to the bottom.
With respect to the apparatus, preferably a heater for heating the process air is arranged below the return surface.
An advantage is that the process air, having already flown through the material on the bottom and/or on the wall and having taken up moisture from the coating medium, then has a higher capability of absorbing moisture through the heating. This avoids remoisturing of the material during return flow along the return surface and instead an effective drying of the coating medium is achieved.
In a further preferred embodiment of the method, the material is discharged through its centrifugal motion.
The feature has the advantage that the material can be automatically removed from the container after ending of the treatment process.
In a further preferred embodiment of the apparatus, an upper edge of the wall of the container is curved radially inwardly.
The feature has the advantage that the product receives a change in direction of movement and is guided to the return surface along the radially inwardly curved edge of the wall of the container, this through constructively simple measures.
In a further preferred embodiment of the apparatus, an annular guide element is arranged within the container in its upper peripheral region, which is radially spaced from the wall of the container and connected thereto, so that a radially inwardly curved passing gap is formed for the moving material between the annular guide element and the upper peripheral region of the wall.
The feature has the advantage that the material can emerge in the direction of the return surface in a predetermined layer thickness between the annular guide element and the upper radially inwardly curved edge of the wall of the container. Thus the material flows onto the return surface with a defined particle density and subsequently flows pass the spray nozzle. The thrust of the material flowing along the wall upwardly due to centrifugal forces provides a sufficient exit thrust for the material through the passageway or gap.
In a further preferred embodiment of the apparatus, the annular guide element is connected to the wall of the container by means of several guide blades, wherein the guide blades are curved backwardly in rotational direction as seen from bottom to top.
The feature has the advantage that the guide blades in the upper region of the container allow a further mixing of the material before the material falls onto the return surface. In addition, the guide blades together with the mentioned discharging of the material through centrifugal motion allow an automatic conveyance of the material out of the container.
In a further preferred embodiment of the apparatus, a stationary closure ring is arranged above the container extending radially inwardly from the edge of the container and gliding on the edge of the wall.
This closure ring, in particular in conjunction with the before mentioned guide blades, is of advantage because the guide blades deflect the material against the stationary closure ring thereby slowing down the material which favors the falling of the material down onto the return surface.
In a further preferred embodiment of the apparatus, a discharging device is provided for discharging the container comprising an annular space surrounding the container in which a chute is arranged surrounding the container in helical manner, whose upper end is arranged in the region of the edge of the wall of the container.
With this configuration of the discharging device, the possibility is provided to remove the material from the container with centrifugal motion in constructively simple manner. The chute can be equipped with one or more agitators to accelerate the flow of material along the chute.
In a further preferred embodiment, the closure ring closes the upper end of the chute.
The advantage is that it is guaranteed that the material does not inadvertently escape the container during the treatment process.
In a further preferred embodiment, the closure ring can be displaced upwardly away from the edge of the wall.
The feature has the advantage that the closure ring is driven upwardly from the edge of the wall for discharging the material from the container, so that the mentioned guide blades can convey the material under centrifugal motion out of the container.
In a further preferred embodiment, an axially actuatable inlet/outlet air valve is arranged in the annular space of the discharging device.
The feature has the advantage that with the inlet/outlet air valve, either a ventilation and de-dusting of the discharging device is possible with the air or, when switching the valve to inlet air, the material is supported by the inlet air in its discharging motion, wherein the air permeable chute is fluidised.
In a further preferred embodiment of the apparatus, a ring collar is arranged between the spraying device and the return surface, which is radially spaced at a small distance from the spraying device.
The feature has the advantage that the ring collar together with the return surface acts as a funnel-like guide for the material. This guarantees that the material passes by the spray nozzle at a distance at which the coating medium is completely atomized and thus can be optimally applied to the material.
Further advantages can be taken from the following description and the attached drawings.
It will be understood that the above-mentioned and following features are not only applicable in the given combination, but may be used in other combinations or taken alone without departing from the scope of the present invention.
Selected embodiments are shown in the drawings and will be described in more detail below.